Mac Monitor screen isn't full size

I started playing Sims 3 on my MacBook Pro laptop and it was working fine. Then it froze on me one time but my laptop still worked. But when I shut down my laptop and turned it on again the actual monitor screen doesn't fit the full 13". It only goes about 11". First off, is this because of my Sims game that it did this? Because it never did it before. Secondly, is there a way I can make my screen fit the full 13" or do I need to take it into an Apple store?